1. Field of the Invention
This invention relates generally to an apparatus used for digital painting or printing and, more specifically, to an apparatus that employs a metering device for metering a quantity of paint to be deposited on a surface to be painted or printed and that deposits the metered quantity of paint or other pigmented liquid material on the surface.
2. Background of the Invention
As computer technology has advanced, the ability to view high resolution graphics on a computer monitor or other visual display device has improved, and the capacity to reproduce these high resolution graphics onto a tangible medium has improved in both resolution, quality, and speed. One of the more significant and lucrative color printer technologies to be developed in recent years is the ink jet printer, which mixes several colors, typically cyan, magenta, yellow and black, on the print medium (e.g., paper) to form a color image. Conventional ink jet printing heads include a plurality of nozzles and thermal elements. Ink is expelled from the nozzles in a jet by bubble pressure created by heating the ink with the thermal elements while the nozzles and thermal elements are in close proximity. One such ink jet printing head, as described in U.S. Pat. No. 5,121,143 to Hayamizu, includes a thermal head member having at least one thermal element consisting of a plurality of thermal dot elements and a plurality of electrodes of different widths connected to each thermal element whereby different widths of heated portions of the thermal element are obtainable to vary the amount of ink jetted in one dot. Another such ink jet printing head is described in U.S. Pat. No. 4,731,621 to Hayamizu et al.
Another type of print head is disclosed in U.S. Pat. No. 4,764,780 to Yamamori et al. in which an ink ejection recording apparatus includes a plurality of ink ejection heads connected to an ink tank. Each of the ink ejection heads have an ink nozzle through which minute ink droplets are discharged in accordance with an electric signal. An air nozzle opposing the ink nozzle and adapted for forming an air stream accelerates the ink droplets toward a recording medium.
A conventional airbrush is manufactured by the Paasche Airbrush Co. In Harwood Heights, Ill. The airbrush employs a reciprocating needle that retrieves paint from a reservoir and exposes the paint on the needle to a jet of air. The paint is blown from the needle and onto a print medium. Metering of the paint, however, is manually controlled by pressing a finger lever to allow air to flow through the airbrush.
Typical desk top ink jet printers for home or office use are relatively inexpensive but are usually limited to printing on standard office size sheets of paper, such as 81/2.times.11 or similar standard sizes. Printers that can accommodate larger formats such as poster-sized sheets, however, are currently thousands of dollars to purchase. Printing machines that can print billboard-sized sheets are typically tens of thousands of dollars to purchase.
Some wide format printers are able to accommodate 16 feet or wider substrates, such as films, paper, vinyl, and the like, and can print 300 ft.sup.2 per hour, depending on the resolution of the print. Such machines sometimes employ piezo printhead technology that employs several printheads per color with numerous nozzles per printhead to deposit ink onto the print medium. Another approach is to employ air brush technology in which inks are metered by valves and/or pumps and deposited onto the substrate. The quantity of ink pumped for each color and the position at which it is deposited on the print medium is typically computer controlled. The print medium is typically provided on a roll in which unmarked medium is fed under the print head and printed medium is re-rolled once the ink has had sufficient time to dry. Large format printers using air brush technology typically have a resolution of up to 70 dpi.
In addition to the cost of the machine itself, which employs relatively small orifices, valves and nozzles for depositing the desired quantity and color of ink on the print medium (e.g., paper), very fine grade inks are used in which particle sizes within the inks are kept to a minimum to help keep the orifices, valves, and nozzles of the ink system from becoming clogged. Such inks are expensive and are not very cost effective for painting or printing billboard sized images. Despite the high quality and expense of ink products, clogging of the printhead is still a problem in current printer technologies.
Many large format printers also use water-based inks that may not be suitable for outdoor use. Accordingly, special waterproofing systems and techniques must be employed, such as treating the printing medium with a substance that binds with the ink once deposited to form a waterproof mark or laminating the print with a weatherproof film. These weatherproofing techniques and processes add expense to the cost of each print.
Thus, it would be advantageous to provide a paint injector or print head employed in a digital printer that does not include orifices and/or nozzles through which the ink or paint must flow and, thus, is not limited by paint particle size or large particle contamination and is relatively insensitive to the physical properties of the paint. It would also be advantageous to provide a device that can utilize paints and inks already designed for the sign and art industries and that can be employed to digitally print on large format media.